Liquefaction of methane (LNG) is well established, dating back to over 50 years. In certain cases, liquid ethane can also be produced directly from these LNG plants along with other higher hydrocarbon chain components and are called natural gas liquids (NGLs). However, many applications require the independent liquefaction of a gaseous ethane stream from a pipeline.
As such, there is a demand to liquefy a pressurized gaseous stream from a pipeline containing primarily ethane; however, this stream typically contains small amounts of methane (˜3% vol), propane, ethylene and other components. Once liquefied, this fluid can be transported by truck or ship to distant locations where it is processed or “cracked” into ethylene; however, in order to ship in this manner, the methane content needs to be reduced to the range of ˜0.5% vol methane. This creates a significant problem, since the gaseous ethane stream must be cooled to a temperature to allow for liquefaction of ethane, while also adding heat to vaporize off the methane.
Therefore, it would be desirable to have an improved process for liquefaction of a gaseous stream comprised predominantly of ethane that was simple and efficient.